The invention is directed to a dental handpiece arrangement which has a drive transmission including a first and second drive shaft section for transmitting rotary motion from a drive motor to an acceptance sleeve or chuck which receives and rotatably supports a dental tool in the head housing of the handpiece arrangement. In order to obtain a different drive relationship, the first drive shaft has a pair of coaxially arranged gears of different number of teeth so that a different ratio is obtained between the first and second shaft depending on which of the two gears of the first shaft is engaged.
A dental handpiece, which has a drive shaft that is connected to the motor and terminates in a pair of coaxially aligned gears of different number of teeth and has a second drive shaft having a gear engaging one of the pairs of gears, is known and an example is disclosed in U.S. Pat. No. 3,229,369. As disclosed in this patent, the axis of the drive train is divided transversally once along the longitudinal axis of the handpiece so that the two drive shaft sections with gear teeth lying in between are formed. The gear arrangement consists of two coaxial drive gears having mutually different numbers of teeth which are arranged at the end of one drive shaft section essentially in one plane and an individual drive gear arranged on the end of the other drive shaft. By means of interchanging or adjusting the front or head handpiece part relative to the back or rear part, a step-up or step-down of the drive speed can be achieved so that a change in speed of the drive axle can only be undertaken in one transmission direction by means of an interchange or adjustment. For example, from a direct transmission with a transmission ratio 1:1 to a stepped-up with a stepped ratio of 1:3 or from a direct transmission to a stepped-down with a stepped-down ratio of 3:1. In the case of the step-down, the changeable gears is situated in a removable head part together with two coaxial drive gear wheels. In the case of stepped-up, these gear parts are situated in the handpiece part on the drive side. For a stepped-up and a stepped-down of the speed, different drive motors or respectively drive side handpiece parts with appropriately designed drive shaft sections must be provided. Since a Dentist works with both a stepped-down as well as a stepped-up drive speed, he must have a plurality of drive motors or respectively drive side handpiece parts in accordance with the known handpiece arrangements.
Another disadvange of the known handpiece arrangement or design is that the gear wheels required for the gear stepping generally increases the outer diameter of the handpiece parts particularly in the area of the bend given to the angle pieces. In addition, no rotation of the handpiece with respect to the drive part is possible because of the possibility of changing the position of the head part and thus the gear ratio.
In addition, it has proven expedient for the angled handpiece to have a counter bend of approximately 20.degree. with respect to the longitudinal axis of the handpiece. This counter bend is too abrupt and in conjunction with the enlargement of this area as mentioned above, adversely affects the manipulation of the handpiece.